The press were travelling on a separate plane to the president

The man, who flew from South Africa to Uganda, also succeeded in entering a restricted compound on the shores of Lake Victoria, where Mr Bush was meeting his Ugandan counterpart, President Yoweri Museveni.

Members of the US secret service were tipped off about the unidentified man by a White House aide, said deputy secret service director Mark Sullivan.

Although the man was not carrying any weapons, and reportedly never had access to the president, correspondents say his presence on the flight is an alarming security gaffe.

Motive unknown

"He did not have a credential. He did not have a passport. He has nothing," White House travel office official Curtis Jablonka said.

"There was no indication the stowaway came within sight of President Bush," Mr Jablonka added.

The chartered United Airlines Boeing 747, flying from Pretoria, was carrying 130 members of the press and White House staff.

After his detention, the man began shouting as he was led away and driven off in the back of a white sports utility vehicle.

Ugandan police spokesman Asuman Mugenyi said the man was South African:

"He claims he's a journalist, but he was not entitled to be with the advance party of the president," Mr Mugenyi said. "We've not established his motives."